Re: Arbiter Question, IRDY#, FRAME#

["Peter Marek" <peter.marek@marekmicro.de>]

James,

arbiters usually need to monitor IRDY and FRAME to recognize broken masters:

1) Broken masters may assert REQ and will not start a bus cycle (drive FRAME
active)
2) In PCI, Masters need to start to drive the bus 16 clocks after GNT has
been asserted AND the bus is idle. The arbiter implements a timeout counter
for watching this period.
3) Note, that there's some time in between thge assertion of GNT and the
time the master may start driving the bus.
this is due to the fact that PCI bus arbitration is hidden behind data
transfers on the bus. The "old" master may still be driving the bus, when
the "new" master is asserted GNT. Thus, the new master has to wait until the
old master has stopped driving the bus. This stime is depending on latency
timer settings, etc.
4) Consequently, the arbiter may no start the timeout counter for the new
master before the old master has finished driving the bus, i.e. the ībus is
idle.
5) The bus idle state may only be detected using FRAME and IRDY: The bus is
idel if FRAME is high and there's a rising edge on IRDY.
6) That's why arbiters need to connect to IRDY and FRAME.

regards,


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Peter Marek
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----- Original Message -----
From: James Murray <jmurray@triscend.com>
To: PCI SIG <pci-sig@znyx.com>
Sent: Wednesday, March 21, 2001 6:01 PM
Subject: Arbiter Question, IRDY#, FRAME#


> Hello
>
> If a PCI arbiter bus parking scheme is to park the bus at the Master
> that last used the bus (was last granted), does it follow that the
> arbiter does not need to take FRAME# and IRDY# as inputs, since it does
> not need to know when the bus goes idle??
>
> Thanks
>
> James